I need to split the crankcase soon any advice on doing this?

[taysidedragon]

I have safely removed all of the pistons - when I came to mark them with a cylinder number on the inside of the skirt I found that they had been done before albeit in my view back to front.
To me number 1 cylider is on the nearside (left) of the bike with number 4 cylinder on the offside (right / clutch side). There is the possibility that they were put in back to front - that might explain the poor cold compressions.

I've dismantled 2 400f engines and they were both numbered back to front like yours. I wouldn't worry about it too much. As long as the same person took them out and put them back they should be in the right place.
When I cleaned up my pistons and measured them there was too much wear in the ring slots and they had to be replaced anyway. You may find the same.

[McCabe-Thiele (Ted)]

I have safely removed all of the pistons - when I came to mark them with a cylinder number on the inside of the skirt I found that they had been done before albeit in my view back to front.
To me number 1 cylider is on the nearside (left) of the bike with number 4 cylinder on the offside (right / clutch side). There is the possibility that they were put in back to front - that might explain the poor cold compressions.

I've dismantled 2 400f engines and they were both numbered back to front like yours. I wouldn't worry about it too much. As long as the same person took them out and put them back they should be in the right place.
When I cleaned up my pistons and measured them there was too much wear in the ring slots and they had to be replaced anyway. You may find the same.

I've now decided to have a rebore as it would be daft not to now that the engine is being fully dismantled -  the cold compressions were pretty poor plus there is a lip on the cylinder bores.
A case of do it once; do it right.

[Bryanj]

Lip on the  bore? You may need 2nd o/s (0.5mm)  you dont often see lip on Hondas even over 100,000 mile ones

[McCabe-Thiele (Ted)]

Lip on the  bore? You may need 2nd o/s (0.5mm)  you dont often see lip on Hondas even over 100,000 mile ones

I'll leave that to Trigger when the block arrives tbh it was what I thought was normal at the top of the cylinder.
As I know the pistons have been out before there it might not be the original block who knows after 42 years?

[McCabe-Thiele (Ted)]

Lip on the  bore? You may need 2nd o/s (0.5mm)  you dont often see lip on Hondas even over 100,000 mile ones

Turns out the lip was carbon deposits - bores showed signs of previous partial seizure & freeing off probably from years of storage - having +0.25 rebore.

I have removed the  external gear shift mechanism so once I have prepped the various bolts ready for removal I will seperate the halves early next week - provided it stays warmish.

I'm going to make a small wooden support frame for holding the engine casing upside down to make seperation easier. (I am a hoarder of wooden offcuts.)